Great Ape Isotope Ecology Lab

The vast majorities of remaining populations of apes in Africa are not habituated to human observers and experience considerable decline in numbers. To obtain important answers about the biology, diet and tool use before it is too late, we are applying stable isotope analysis to a large array of populations. In close collaboration with the Light Isotope Mass Spectrometry Laboratory of the Departments of Human Evolution, we have been working on several projects using stable isotope techniques (δ13C, δ15N, δ34S). These projects involve both wild and captive study subjects. The main aim of the collaboration is to apply methodologies that are well-known from archaeological sciences to reconstruct the dietary behavior of extant African apes. The essential question concerns the significance of meat-eating, insectivory, and nut-cracking in chimpanzees and bonobos. Additionally, isotope studies on captive apes allow us to investigate the possibilities and limitations of stable isotope analysis in detecting physiological responses to e.g. nutritional stress and meat-eating. For isotope analysis, a rich variety of sample materials, including hair, urine, bone, chitin and plant fibers can be obtained from the field.

Initial research on habituated apes included studies on the isotope ecology of the Lui Kotale bonobos (Pan paniscus) from Salonga National Park in the Democratic Republic of Congo, as well as a study on the meat-eating behavior of the Taï chimpanzees (Pan troglodytes verus) of the Côte d’Ivoire. These studies confirmed that stable isotopes can provide novel information on dietary composition, feeding niche utilization and dietary variation over time. This information is particularly useful in unhabituated apes, where isotope ratios are measured in hair samples collected non-invasively from sleeping nests. Due to its constant growth, hair has the property to retain a temporal dietary signal and does not change its primary biochemical composition. Data obtained from hair is related to plants and animals from the local habitat to reconstruct the trophic level within the food web and to characterize the specific feeding niche. We also study the isotopic composition of bone collagen obtained from skeletal collections of the Taï chimpanzee collection housed at our institute, to study long term effects of dietary behaviour. Our main objectives in the study of great ape isotope ecology is to address questions on

hunting and meat eating behavior

nut and insect consumption as indicators for tool use behavior

inter-group variability in diet reflecting ecological adaptations

intra-group variability indicating social or sex determined differences in diet

dietary seasonality

utilization of fall back foods and their relevance in ape diet

the integration of other isotope systems (δ34S, 87Sr/86Sr, δ18O) in the study of primates

Figure 2: Isotope ecology of a tropical rainforest (Salonga National Park, D.R.C.). Measuring stable isotopes (carbon isotope ratio = δ13C, nitrogen isotope ratio = δ15N) in animals living in the habitat of great apes is important for the differentiation of ecological feeding niches in the environment.

Figure 3: Collagen extraction for isotope analysis. In skeletal remains the mineral fraction of bone is demineralized and only the organic fraction (collagen) is used for analysis.